Fracture treatment system for wells

Abstract

A well fracturing system in which a fracturing fluid storage vessel, high pressure pump and high pressure conduit are connected in series to a well. A pressure vessel is connected to the high pressure conduit for injecting proppant carrying fracturing fluid into the well without the proppant carrying fracturing fluid passing through the high pressure pump. The pressure vessel may be formed of a pipe with a free floating piston dividing the pressure vessel into a drive side and driven side. Proppant carrying fracturing fluid is stored in the driven side, and may be emplaced within the pressure vessel at a remote site from the well. Drive fluid is injected into the drive side to force the proppant carrying fracturing fluid into the high pressure conduit and down the well. The drive fluid may be a diverted portion of fracturing fluid pumped by the high pressure pumper. Several pressure vessels may be used in parallel, and proppant may be stratified in the pressure vessel.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. An apparatus for fracturing a formation penetrated by a well, the apparatus comprising: a fracturing fluid storage tank;   a high pressure pumper having a pump inlet operably connected to the fracturing fluid storage tank and having a pump outlet;   a high pressure conduit leading from the pump outlet to the well;   a pressure vessel having a vessel outlet connected by a line to the high pressure conduit;   dispensing means for dispensing fluid from the pressure vessel into the high pressure conduit; and   means for regulating flow in the high pressure conduit.   
     
     
       2. The apparatus of claim 1 in which the dispensing means comprises: a movable piston disposed in the pressure vessel and separating the pressure vessel into a drive end and a driven end, the driven end including the vessel outlet; and   drive means for driving the movable piston towards the vessel outlet.   
     
     
       3. The apparatus of claim 2 in which the drive means comprises supply means for supplying fluid from the high pressure pumper to the drive end of the pressure vessel. 
     
     
       4. The apparatus of claim 3 in which the supply means comprises: a diverter on the high pressure conduit for diverting a portion of flow in the high pressure conduit to the pressure vessel.   
     
     
       5. The apparatus of claim 4 in which: the diverter has first and second outlets; and   fluid flow in the first and second outlets is controlled by first and second valves respectively.   
     
     
       6. The apparatus of claim 5 in which the supply means comprises: control means for opening one of the first and second valves while closing the other of the first and second valves.   
     
     
       7. The apparatus of claim 1 in which the pressure vessel has sufficient volume to complete fracturing a formation without being recharged. 
     
     
       8. The apparatus of claim 2 in which the drive means comprises: a high pressure pump operably connected to the drive end of the pressure vessel.   
     
     
       9. The apparatus of claim 1 further comprising: a pressure sensor sensitive to pressure in the high pressure conduit;   a bypass circuit connected to the high pressure conduit and connected to the fracturing fluid storage tank to return fluid from the high pressure conduit to the pump inlet;   a bypass valve on the bypass circuit; and   a controller responsive to the pressure sensor for opening the bypass valve when the pressure in the high pressure conduit exceeds a pre-set amount.   
     
     
       10. The apparatus of claim 1 in which the pressure vessel has a drive end and a driven end, the vessel outlet being at the driven end, and an inlet being at the drive end, the dispensing means comprising drive means to supply drive fluid to the drive end of the pressure vessel through the inlet. 
     
     
       11. The apparatus of claim 10 in which the drive means comprises a second high pressure pumper connected to supply fluid to the drive end of the pressure vessel. 
     
     
       12. The apparatus of claim 11 in which the dispensing means comprises a movable piston disposed in the pressure vessel and separating the drive end from the driven end. 
     
     
       13. The apparatus of claim 1 further comprising: a second pressure vessel having an outlet connected to the high pressure conduit; and   second drive means for driving fluid from the pressure vessel into the high pressure conduit.   
     
     
       14. A method of preparing a proppant carrying fracturing fluid for use in fracturing wells, the method comprising the steps of: admixing gelation chemicals with a fracturing fluid:   mixing proppant with the fracturing fluid to form a proppant carrying fracturing fluid such that the proppant is uniformly distributed within the fracturing fluid; and   storing the proppant carrying fracturing fluid in a pressure vessel whereby the fracturing fluid forms a gel in the pressure vessel.   
     
     
       15. A method of fracturing a formation penetrated by a well, the well being located at a well site, the method comprising the steps of: creating a proppant carrying fracturing fluid at a site remote from the well site;   storing the proppant carrying fracturing fluid in a pressure vessel;   transporting the pressure vessel to the well site; and   injecting the proppant carrying fracturing fluid into the well.   
     
     
       16. The method of claim 15 in which fracturing the formation is completed without recharging the pressure vessel. 
     
     
       17. The method of claim 15 in which the pressure vessel has a drive end and a driven end, and in which the proppant carrying fracturing fluid is stored in the driven end of the pressure vessel. 
     
     
       18. The method of claim 17 further comprising: forming a first stream of a proppant free fracturing fluid; and   driving the proppant carrying fracturing fluid from the driven end of the pressure vessel into the first stream to form a fluid for injection into the formation at a rate and pressure to cause fracturing of the formation.   
     
     
       19. The method of claim 18 in which driving the proppant carrying fracturing fluid comprises pressurizing the drive end of the pressure vessel. 
     
     
       20. The method of claim 19 in which the pressure vessel is pressurized with a drive fluid without mixing of the drive fluid and the second fracturing fluid. 
     
     
       21. The method of claim 20 in which the drive fluid is the proppant free fracturing fluid. 
     
     
       22. The method of claim 21 in which the pressure vessel is pressurized by diverting a portion of the first stream. 
     
     
       23. The method of claim 22 in which the drive end of the pressure vessel is separated from the driven end by a movable piston, and the drive fluid acts upon the movable piston. 
     
     
       24. The method of claim 18 in which the first stream comprises a mixture of one or more gases. 
     
     
       25. The method of claim 24 in which the mixture of one or more gases is selected from the group consisting of methane, ethane and nitrogen. 
     
     
       26. Apparatus for storage and injection of proppant containing fracturing fluids, the apparatus comprising: a pressure vessel having an inlet end and an outlet end;   a movable fluid dividing interface disposed within the pressure vessel, the movable fluid dividing interface being movable from the inlet end towards the outlet end and dividing the pressure vessel into a drive side and a driven side; and   a port for filling the driven side of the pressure vessel.   
     
     
       27. The apparatus of claim 26 in which the pressure vessel is cylindrical. 
     
     
       28. The apparatus of claim 27 in which the movable fluid dividing interface is a free floating piston. 
     
     
       29. The apparatus of claim 28 in which the outlet end comprises an off axis outlet. 
     
     
       30. The apparatus of claim 26 in which the driven side of the pressure vessel is filled with proppant carrying fracturing fluid. 
     
     
       31. The apparatus of claim 26 in which the pressure vessel further includes a driven side drain valve for draining the driven side of the pressure vessel. 
     
     
       32. The apparatus of claim 26 in which the pressure vessel further includes a drive side drain valve for draining the drive side of the pressure vessel. 
     
     
       33. The apparatus of claim 26 in which the pressure vessel has sufficient volume to hold fluid for a single well fracturing operation. 
     
     
       34. The apparatus of claim 26 in which the pressure vessel has a volume in excess of 5 cubic meters. 
     
     
       35. A method of fracturing a formation penetrated by a well, the well being located at a wellsite, a pressure vessel being located at the wellsite, the pressure vessel having a drive end and a driven end, the method comprising the steps of: forming a first stream of a first fracturing fluid; and   driving a second fracturing fluid from the driven end of the pressure vessel into the first stream to form a fluid for injection into the formation at a rate and pressure to cause fracturing of the formation.   
     
     
       36. The method of claim 35 wherein the second fracturing fluid has proppant distributed within the second fracturing fluid. 
     
     
       37. The method of claim 36 in which driving the second fracturing fluid comprises pressurizing the drive end of the pressure vessel. 
     
     
       38. The method of claim 37 in which the pressure vessel is pressurized with a drive fluid without mixing of the drive fluid and the second fracturing fluid. 
     
     
       39. The method of claim 38 in which the drive fluid is the first fracturing fluid. 
     
     
       40. The method of claim 39 in which the pressure vessel is pressurized by diverting a portion of the first stream. 
     
     
       41. The method of claim 40 in which the drive end of the pressure vessel is separated from the driven end by a movable piston, and the drive fluid acts upon the movable piston. 
     
     
       42. The method of claim 35 in which the fracturing of the well is completed by a single cycle of driving fluid from the pressure vessel without recharging the pressure vessel. 
     
     
       43. The method of claim 35 in which the first stream comprises a mixture of one or more gases. 
     
     
       44. The method of claim 43 in which the mixture of one or more gases is selected from the group consisting of methane, ethane and nitrogen.